A prototype, literally is anything that was not intended for mass-production. Under this category we include unfinished ponies, factory faults, market testers, and often even "hybrids", before evidence of their mass-production is found.

Because of their particular nature, information on these item is little.

I have listed here a few specimens from my own collection, all being symbol-less (unfinished) ponies: they may either be seen as prototypes/testers or factory faults.